Low-voltage gas discharge illumination device



Feb. 4, 1958 G. VMAURER 2,322,496

LOW-VOLTAGE GAS DISCHARGE ILLUMINATION DEVICE Filed Dec. 5, 1956 Tint. "3.

72 IN VEN TOR.

65026 M/zuem BY @W ATTO Q/VL S LOW-VOLTAGE GAS DISCHARGE ILLUMINATION DEVICE Georg Maurer, Berlin-Tempelhof, Ger-many Application December 5, 1956, Serial No. 626,376

' 8 Claims. 01. 313-188) United States Patent Heretofore illuminating tubes of the types used in adi vertising and display signs filled with neon, argon, and the like have required inter-electrode voltages of thousands of volts to cause ignition or ionization of the contained gas or vapor. This voltage requirement necessitated the use of high voltage generating equipment with such apparatus, 'With the attendant disadvantages of a relatively high cost of installation and operation, danger to personnel, a sensitivity to atmospheric conditions, and a tendency to arc-over and short circuit, as well as other drawbacks well known and recognized by those skilled in the art.

Furthermore, by virtue of the high voltage requirements, it has been found impracticalwith such prior devices to attempt to use them to produce travelling light or chasing effects because of, for example, the arcing ditficulties experienced in switching at such high voltages.

With sufficiently short tube lengths, ignition voltages below a thousand volts were known to 'be possible, but the operational life was in general too short to he economically feasible for the above purposes.

As a consequence, such devices as neon tubes and the like, which can be rapidly ignited and extinguished by appropriate switching of the voltage supplied to their electrodes, have been practically inaccessible for use in travelling signs, and resort :has been had, out of necessity, to low voltage incandescent lamps for such purpose, which,

because of their heated filaments, cause an rafter-glow effect that detracts considerably from the travelling or chasing effect desired.

An object of the present invention is to provide .an

illumination device of the electric gaseous discharge type for use in advertising and display signs and thelike which can be operated at much lower voltages than heretofore found possible for similar devices;

Another object is to provide such a low voltage electric gaseous discharge device for use in advertising and display signs to :produce travelling and chasing effects without undesirable after-glow;

A further object is to provide such a device which can "be installed and operated without need for high voltage generating equipment;

Another :object is to provide such an electric gaseous discharge device .having an exceptionally long operational life; and

.An additional object is -to provide a low voltage device of the above type having an envelope which is translucent or even transparent throughout its entirety.

Briefly the .present invention comprises an illumination device of the electric gaseous discharge type having an envelope filled with neon gas or the like which is comextend in respective straight sections well-known materials Eemployed prised of an elongated auxiliary tube, an elongated neutral wire electrode disposed longitudinally within such tube and having an external electric terminal means, a plurality of spaced stub projections disposed along said tube each with an electrode therein having a lead wire extending through the envelope to permit external electrical connection thereto, and an electrically conductive shield or coating on the outside surface of the envelope which jcovers a substantial portion of the surface, but which .is Ztransparent or translucent or. which leaves an exposed portionon each of said stub projections to allow transmission ;of the illuminating glow from within. The coating terminates sufiiciently short of all of the lead wires of all the electrodes except .the neutral wire electrode (to which it may be directly connected), to prevent short'c'ircuiting of the ignition current as will be explained ingreater detail hereinafter. The coating is normally maintained at approximately ground potential, or the potential of the neutral wire electrode, and a relatively low voltage can be applied between the latter electrode and any of the other electrodes as desired to produce .an illuminating glow there'between. Chasing effects without after-glow can be produced by sequentially igniting successive segments of the device with an appropriate switching means.

Other objects and features of this invention will become apparent in the following description and appended claims as Well as in the drawings.

In the drawings;

Fig. 1 is a partially sectioned perspective view of .one embodiment of the present invention;

Fig. 2 is a partially sectioned perspective-view of another embodiment; and r Fig. 3 is a simplified schematic electrical wiring diagram showing one arrangmcnt for energizing the appara- Ius of Fig. 1.

Referring to Fig. 1, one embodiment oft-he present invention is shown comprising an elongatedenvelope 1:0 constructed of glass and sealedto-confine a ,gas .ofrelatively low ionization potential such as neon, argon, and the like. Theenvelope 10 has :anauxiliary .orreservoi-r tube 11 of generally cylindrical shape, and disposedalong the length thereof and communicating therewith are a plurality of spaced tubular stubs or projections .lzwvhich .13 generally perpendicularly therefrom, then havecurved .or-circular extensions 14 disposed in a plane perpendicular to the straight sections 13, and finally terminate inan-gularly-disposed end sections .15 each carrying an inner electrode '16 having an associated external .electric terminal means 1.7 as shown. V

The above angular orientation of the .stubsl-Z and "the shapes of the various sections thereofare .of course given by way of .exampleand *can-be of anyrconvenient form as desired, .such .as, for example, letters of the .alphabet.

' The electrodes can be constructed of any .ofthe usual for such purposes (e. .g. can :be coated With any materials such as cesium .iron, nickel, etc.;) and desired of the :known low work :funotion onnxygenfand thelilce. I

An elongated el eetrode or neutral wire 38 is disposed longitudinally within the auxiliary tube =11; having both of its ends 19;, 20 supported therein :by a y.;ccnven ient means such as. glass bead protuberances Ino't shown)- extendin'ginwardly from the internal end surfaces, .21, .22 thereof, one Of the ends 22 having .an electric terminal m ans or lead wire 23 extending externally of the envelope 10 to provide 'forconnection to a voltagesource .(hot shown). 1 On. the external suriace24 .of. the envelope l9 .i's'an electrically conductive layer, covering -.or.coating.25,,.which is connected to the neutralwire 1'8 and which covers such surface 24, including the auxiliary tube 11, the straight sections 13 and end sections 15 of the stubs 12 (except for the areas 26 adjacent the electrodes 16), and also including the rear half of the external surface of the curved extensions 14 as viewed in Fig. 1, leaving an uncovered or exposed portion 27 on the front half of the latter extensions 14. The conductive layer 25 can be any of a number of opaque materials such as tin foil, aluminum foil or other similar electrically conductive metallic material; colloidal graphite dispersed in a vehicle such as shellac which can be hardened after application to form a durable covering, such a material being known commercially as aquadag, and the like; and other substances which can be applied in liquid form and which harden on drying to provide a translucent (sometimes even transparent) electrically conductive film such as water glass (i. e. sodium silicate solution) and the like. It is also possible to use an envelope made of one of a variety of electrically conductive glasses, or ordinary glass can be treated with cupric chloride in a manner already known to provide it with an electrically conductive outer surface that is transparent or translucent.

When either the above translucent type of film, or a glass with an electrically conductive translucent outer surface is used, it is permissible and even preferable to render the entire external surface of the envelope conductive with the exception, of course, of those areas immediately adjacent the stub electrodes which must be non-conductive to prevent short-circuiting. With the other types of opaque coatings, however, an uncovered or exposed portion of the external surface must be retained to provide the desired illumination. Of course in the latter instance such portion not covered by the opaque coating can be treated with one of the above translucent materials to further improve the operational performance of the device.

Electrically conductive" as used in this description and the appended claims means having a virtually negligible resistance to the passage of an electric current, either electrostatic or electro-dynamic, and in particular to the conduction of the positive charges or wall charge away from the internal surface of the envelope 10, or the conduction of electrons to the latter surface from an external source to neutralize such positive charges, whichever the case may be.

It is possible to use combinations of two or more of the above conductive materials at one time. For example, the water glass can be employed as an adhesive binder for maintaining the metallic foil in place on the envelope l0, and then aquadag or a silver powder shellac can be applied over the foil if desired.

As an additional feature, the interior surface 28 of the envelope 10, or at least that portion underneath the uncovered portion 27, can be coated with a fluorescent material, or fluorphor, to enhance the illumination propensities of the device.

Fig. 2 shows still another embodiment to exemplify another variety of shapes and forms of the invention which may be used. The envelope 29 has an elongated cylindrical auxiliary tube 30 which carries an elongated neutral wire electrode 31 longitudinally disposed therein and having an external electric terminal means 32 at one end 33. Mounted at spaced positions along the auxiliary tube 30 and extending laterally therefrom and in communication therewith are three stub projections 34, 3S and 36. Each has a perpendicularly oriented straight section or trunk portion 37 adjoining the auxiliary tube 30. Two of the stubs 34, 35 are L-shaped, having respective single rightangled branch portions 38, 39 at the outboard ends 40 of their trunk portions 37, one such branch portion 38 being disposed laterally, and the other branch portion 39 being disposed longitudinally, with respect to said auxiliary tube 30. The latter two branch portions 38, 39 have respective end sections 41, 42 disposed in the general direction of the auxiliary tube 30, and the related trunk portion 37, at an acute angle with the associated branch por' tion 38, 39. Located at the free ends 43, 44 of end sections 41, 42 are electrodes 45, 46 having electrical terminal means 47, 48 provided for external electrical connection.

The third stub 36, is identical to the other two in all respects except that it is T-shaped, having a pair of oppositely disposed branch portions 49, 50 at the outboard end 51 of its trunk portion 37, which are oriented parallel to the longitudinal axis of the auxiliary tube 30, and have respective end sections 52, 53 located in a similar fashion to those on the other stubs 34 and 35, and carry electrodes 54, 55 and external electric terminal means 56, 57. The outer end 58 of one branch portion 49 is located close to the outer end 59 of the branch portion 39 of the adjacent stub 35.

In the above embodiment the outboard portions 60 of the branch portion-38, 39, 49 and 50 are provided for illumination, and the remainder of the external surface 61 of the envelope 29, except for those areas 62 immediately adjacent the various stub electrodes, is covered with a metal foil 63, the latter being in turn covered with a silver powder shellac coating 64. Such foil 63 and coating 64 are electrically connected to the neutral wire 31. The interior surface 65 of the outboard portion 60 of each branch portion 38, 39, 49 and 50 is covered with a fluorphor 66 of the usual type.

The operation of devices embodying the features of the present invention, such as the above described embodiments, can be easily efiected in any one of a number of ways as desired utilizing equipment available in the art. Example I A glass device was constructed in accordance with Fig.

1 having the following features:

(a) Total length (auxiliary tube 11), 50 cm. (b) Length of the visible tube parts (curved extensions 14) each, 28 cm.

(c) Outside diameter of glass tubing, 18 mm.

(d) Cross section of neutral wire 18 (two twisted chromium nickel wires), 1 mm.

(e) Gas-% neon+5% argon-t-mercury (f) Gas pressure-6 mm. mercury (g) Conductive coatingsilver foil The device was electrically connected as shown in Fig. 3, with the electric terminal means 17 each connected 'through an 8000 ohm resistor 67 to a separable stationary contact 68 of rotary switch 69. The conductive coating 25 was connected to electric terminal means 23 of the neutral wire 18 as shown and both thence to sliding tap 70 of variable resistor 71, one end 72 of which was connected to one side 73 of the secondary winding 74 of power transformer 75. The other side 76 of the secondary 74 was connected to the sliding contact 77 of rotary switch 69. The primary winding 78 of transformer 74 was connected to a usual -120 volt single phase A.-C. source, which with the circuit shown gave a desired ignition current of about 30 to 50 milliamperes.

, With the sliding contact 77 touching any one stationary 'contact 68, sliding tap 70 was adjusted for the minimum voltage needed for excitation of the portion of the device between the particular interconnected electrode 16 and the neutral wire 18. Such minimum voltage was found 'to be about an average of 330 volts. Similar tests with the silver foil removed showed that the minimum voltage required for similar excitation was on the average of The operational life of the device at the above voltages and currents was found to be of the order of 3000-5000 hours.

By setting sliding tap 70 to provide enough voltage for excitation, movement of the sliding contact 77 of rotary switch 69 across successive of the stationary contacts: 68 in, for example, a counter-clockwise direction as viewed in Fig. 3, caused the ignition of successive segments of the envelope and produced a travelling light eliect moving 'from left to right without any after-glow efiect.

Example 11 Another glass device was constructed in accordance with Fig. 2 having the following features:

(a) Total length (auxiliary tube 30), 45 em.

(b) Length of the visible tube parts (e. g. branch portion (c) Inner diameter of tubing, 16 mm.

(d) Outer diameter of tubing, 18 mm.

(e) Cross section of neutral wire 31 (steel), 6 x 0.6 mm.

(f) Gas95% neon+5% argon+mercury (g) Gas pressure 6 mm. mercury (h) Conductive coating-silver foil painted with silver powder shellac (i) Fluorphor coating on interior surface 65 of the branch portion The minimum voltage required for excitation of any segment of the envelope 29 between the neutral wire 31 and an electrode for one of the branch portions was found to be on the average about 330 volts A.-C. It was discovered that for best results the ignition current should be maintained at or less than 50 milliamperes, and preferably from about 30 to 50 milliampures. The operational life of the device at the above voltages and currents was found to be of the order of 3000-5000 hours.

By a switching apparatus similar to that shown in Fig. 3 for Example I above, this particular device was found to be operable in the same fashion to produce travelling or chasing effects without after-glow, or by simultaneous application of the required voltage to all electrodes, all branch portions 38, 39, 49 and 50 were able to be illuminated at the same time.

The use of the neutral wire electrode as described above permits a drastic reduction in operating voltage for such illuminating devices from over approximately 1000 volts to about 500 volts, and the use of the conductive layer in combination therewith effects a further significant reduction in the operating voltage to such low voltages as 330 volts or even less, as shown above.

It is known in the art that for a clean tube filled with neon or the like and having a pair of spaced electrodes therein, the voltage required to ignite the gas varies inversely to the inside diameter of the tube, although not necessarily as a linear function thereof. The glow discharge is caused by the ionization of the gas within the tube as a result of electron bombardment. The gas molecules thereby become positively charged particles and the interelectrode space within the tube conductive to an electric current, with a resultant illuminating glow being produced.

Positive charges collect on the interior surface of the glass envelope and constitute what is known in the art as a static wall charge, and as the tube diameter decreases, such wall charge exerts an increasing efiect on the plasma, or space charge within the envelope, requiring an increase in voltage applied between the electrodes to produce and maintain ignition.

By the application of the conductive coating or layer to the external surface of the tube or envelope, the buildup of the positive wall charge is diminished or even eliminated. The positive charges are either conducted through the wall of the envelope to the conductive layer, whereupon they are then conducted to ground, or to the one side of the power supply, or are dissipated into the event, presence of the conductive layer permits, as pref The above effects may not be enough toaccount for the astonishing low voltage operation of the described devices. The theory of operation of the devices is not understood, however, a possible factor in that operation may be the interconnection of the extensions or studs with the elongated envelope which carries the neutral Wire. Due to such interconnection, all parts are bathed in the common contained gas, and when one portion of the system is lit, it is noticed that a glow extendsalong all or most of the neutral wire and elongated envelope, whereby it appears that those portions of the gasin the neighboring unlit-extensions or stubs may be pre-ionized or predisposed for ignition when the current is switched into those port-ions.

The marked improvement in the operating .life of a device made in accordance with this invent-ion, having-the auxiliary tube as described is believed to be due to the substantial increase in the gas volume of the envelope. Such volume is thereby increased from about twentyto about forty percent or more, and the operating life has been found to be increased, for example, fromabout 500- 600 hours to about 3000-5000 hours, or even longer. This increase in operating life andfsignificant lowering of operating voltages has brought the electric dischargetype device within the realm of practicability for commercial use. Thus, with the present invention, it has now become possible to utilize low-voltage gas discharge tubes in travelling and other types of signs, with the benefit of better performance and less expense of installation and operation, and the eliminationof the manifold disadvantages above noted for high voltageinstallations and incandescent lamps.

it is to be understood that the. above embodiments have been described by way of example only,-and that certain changes and additions can be madeto the disclosed devices without departing from the scope and spirit of this invention. For example, any of the well-known available gaseous media can be employed to produce the color of illumination desired. The tubing can be shaped to form any of a number of desired shapes (e. g. script .letters, figures, numbers, etc.). The tubing itself can be of square, rectangular, oval, or other cros'sasectional configuration to provide greater or lesser external surface in comparison with inner volume or diameter, as desired to vary the influence of the external conductive coating on the operation of the device. 7

Furthermore, an auxiliary tube with its enclosed neutral wire can be made of any desired length, being straight or curved in whatever shapes needed, and having any number of stubs disposed thereon as required. The external conductive coating can be directly connected to the neutral wire or can be insulated therefrom to afford a choice as to the respective operating voltages to be applied to each of the latter.

These and other variations can be employed without departing from the present inventive concept.

I claim: 7

1. An illuminating device of the electric gaseous discharge type having a gas filled envelope, and being comprised of an elongated tube, an elongated -electrode "disposed longitudinally within said tube and having an electrical terminal means provided for external electrical connection, a plurality of spaced stub projections disposed along said tube at an angular orientation and in communication therewith, each projection having a curved tubular extension and an electrode disposed therein having an external electrical terminal means, the external surface of each said extension having a transulcent portion, and an electrically conductive layer disposed on the external surface of said envelope being transmissive to light at least at each said translucent portion, said layer being electrically insulated from the electrodes in said projections but connected to said elongated electrode.

2. An illuminating device of the electric discharge type having a gas filled envelope, and being comprised of an elongated tube, an elongated'electrode disposed within 'said tube and having an electrical terminal means proof said projections having electrode means disposed therein connected to a respective external electrical terminal means, at least one of said projections constituted by a trunk portion having at least one branch portion ofiset therefrom with an electrode disposed in said branch portion and having external electrical terminal means, the external surfaces of all of said projections having translucent portions located between their respective electrodes and said elongated electrode, an electrically conductive coating on the external surface of said envelope being transmissive to light at least at each said translucent portion, said layer being electrically insulated from the electrodes in said projections but connected to said elongated electrode.

3. An illuminating device of the electric gaseous dis charge type comprising a gas filled envelope having an elongated tubular member, an elongated electrode disposed longitudinally within said tubular member and having an electrical terminal means provided for external electrical connection, a plurality of spaced stub projections disposed along said tubular member at an angular orientation and in communication therewith, each projection having an electrode disposed therein having an external electrical terminal means, the external surface 'of each said extension having a translucent portion between the latter electrode and the said elongated electrode, and an electrically conductive layer disposed on the external surface of said envelope, said layer being electrically insulated from the electrodes in said projections but connected to said elongated electrode.

4. A gas discharge tube comprising a plurality of -stubs disposed at spaced positions relative to one another,

a common elongated tubular portion connected to all of said stubs, whereby an additional gas volume is'provided, an elongated neutral wire electrode longitudinally disposed within said tubular portion and having at least one electric terminal means located externally of said tube, an electrode disposed within each stub at a spaced position relative to said neutral wire electrode and having an external electric terminal means, and an electrically conductive covering on a portion of the external surface of said tube being electrically insulated from each electrode in each stub.

5. An illuminating device of the electric gaseous discharge type comprising a gas filled envelope, having an elongated tubular portion, an elongated electrode disposed longitudinally within said tubular portion and having an electrical terminal means provided for external electrical connection, a plurality of spaced projections disposed along said tubular portion at an angular orientation and interconnecting therewith, each projection having an electrode disposed therein having an external electrical terminal means.

6. An illuminating device of the electric gaseous discharge type having a gas filled envelope, and being comprised of an elongated tube, an elongated electrode disposed longitudinally within said tube and having an electrical terminal means provided for external electrical connection, a plurality of spaced stub projections disposed along said tube at an angular orientation therewith, each projection having a curved tubular extension and an electrode disposed therein having an external electrical terminal means, the external surface of each said extension having a translucent exposed portion and an enclosed portion, and an electrically conductive continuous layer disposed on the external .surface of said envelope save for said exposed portion of each said extension, and save for an area adjacent the electrode in each of said projections.

7. An illuminating device of the electric gaseous discharge type having a gas filled envelope, and being comprised of an elongated tube, an elongated electrode disposed longitudinally Within said tube and having an electrical terminal means provided for external electrical connection, a plurality of spaced stub projections disposed along said tube at an angular orientation and in communication therewith, each projection having an electrode disposed therein having an external electrical terminal means, the external surface of each said extension having a translucent exposed portion and an enclosed portion, and an electrically conductive opaque layer disposed onthe external surface of said envelope save for said exposed portion of each said extension and save for an area adjacent each electrode in each of said projections, and an electrically conductive translucent layer disposed on each said exposed portion.

8. An illuminating device of the electric discharge type having a gas filled envelope, and being comprised of an elongated tube, an elongated electrode disposed within said tube and having an electrical terminal means provided for external electrical connection, a plurality of spaced stub projections disposed along said tube at an angular orientation and in communication therewith, each of said projections having electrode means disposed therein connected to a respective external electrical terminal means, at least one of said projections constituted by a trunk portion havingat least one branch portion ofiset therefrom with an electrode disposed in said branch portion and having external electrical terminal means, the external surfaces of all of said projections having translucent portions located between their respective electrodes and said elongated electrode, and an electrically conductive coating disposed on the external surface of said envelope save for said translucent portions and save for an area adjacent each electrode in each of said projections.

References Cited in the file of this patent UNITED STATES PATENTS Seaman Apr. 29, 1952 

